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Correlated insulator behaviour at half-filling in magic-angle graphene superlattices

Nature (London), 2018-04, Vol.556 (7699), p.80-84 [Peer Reviewed Journal]

COPYRIGHT 2018 Nature Publishing Group ;COPYRIGHT 2018 Nature Publishing Group ;Copyright Nature Publishing Group Apr 5, 2018 ;ISSN: 0028-0836 ;EISSN: 1476-4687 ;DOI: 10.1038/nature26154 ;PMID: 29512654

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Title:
Correlated insulator behaviour at half-filling in magic-angle graphene superlattices
Author: Cao, Yuan ; Fatemi, Valla ; Demir, Ahmet ; Fang, Shiang ; Tomarken, Spencer L ; Luo, Jason Y ; Sanchez-Yamagishi, Javier D ; Watanabe, Kenji ; Taniguchi, Takashi ; Kaxiras, Efthimios ; Ashoori, Ray C ; Jarillo-Herrero, Pablo
Subjects: Boron ; Boron nitride ; Correlation ; Coupling (molecular) ; Electromagnetism ; Electronics industry ; Electrons ; Energy ; Epitaxial growth ; Graphene ; Heterostructures ; Hybridization ; Insulating materials ; Insulation (Heat) ; Interlayers ; Magnetic fields ; Metamaterials ; Misalignment ; Molecular beam epitaxy ; Observations ; Phase transitions ; Properties ; Properties (attributes) ; Spectrum allocation ; Spectrum analysis ; Superlattices ; Superlattices as materials ; Thermal insulation ; Two dimensional bodies ; Unconventional superconductors ; Van der Waals forces
Is Part Of: Nature (London), 2018-04, Vol.556 (7699), p.80-84
Description: A van der Waals heterostructure is a type of metamaterial that consists of vertically stacked two-dimensional building blocks held together by the van der Waals forces between the layers. This design means that the properties of van der Waals heterostructures can be engineered precisely, even more so than those of two-dimensional materials. One such property is the 'twist' angle between different layers in the heterostructure. This angle has a crucial role in the electronic properties of van der Waals heterostructures, but does not have a direct analogue in other types of heterostructure, such as semiconductors grown using molecular beam epitaxy. For small twist angles, the moiré pattern that is produced by the lattice misorientation between the two-dimensional layers creates long-range modulation of the stacking order. So far, studies of the effects of the twist angle in van der Waals heterostructures have concentrated mostly on heterostructures consisting of monolayer graphene on top of hexagonal boron nitride, which exhibit relatively weak interlayer interaction owing to the large bandgap in hexagonal boron nitride. Here we study a heterostructure consisting of bilayer graphene, in which the two graphene layers are twisted relative to each other by a certain angle. We show experimentally that, as predicted theoretically, when this angle is close to the 'magic' angle the electronic band structure near zero Fermi energy becomes flat, owing to strong interlayer coupling. These flat bands exhibit insulating states at half-filling, which are not expected in the absence of correlations between electrons. We show that these correlated states at half-filling are consistent with Mott-like insulator states, which can arise from electrons being localized in the superlattice that is induced by the moiré pattern. These properties of magic-angle-twisted bilayer graphene heterostructures suggest that these materials could be used to study other exotic many-body quantum phases in two dimensions in the absence of a magnetic field. The accessibility of the flat bands through electrical tunability and the bandwidth tunability through the twist angle could pave the way towards more exotic correlated systems, such as unconventional superconductors and quantum spin liquids.
Publisher: England: Nature Publishing Group
Language: English
Identifier: ISSN: 0028-0836
EISSN: 1476-4687
DOI: 10.1038/nature26154
PMID: 29512654
Source: ProQuest One Psychology
ProQuest Central

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Correlated insulator behaviour at half-filling in magic-angle graphene superlattices

COPYRIGHT 2018 Nature Publishing Group ;COPYRIGHT 2018 Nature Publishing Group ;Copyright Nature Publishing Group Apr 5, 2018 ;ISSN: 0028-0836 ;EISSN: 1476-4687 ;DOI: 10.1038/nature26154 ;PMID: 29512654

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